1. Field of the Invention
The invention is directed to a method for manufacturing heat-shrinkable articles made of a thermoplastic material on which a shape memory is impressed by introducing molecular orientations and molecular structures.
2. Description of the Prior Art
European Patent Application 0 241 776 discloses a method for manufacturing a thermoplastic part having shape memory wherein the shape memory is impressed by a pressure stretching method. With this method, molecular orientations that are fixed at a defined temperature are introduced into a preform in shape-stable condition under the action of pressure. Given the later application of heat, the resultant deformed part attempts to return to its original shape.
In such a method, as well as in the traditional methods for manufacturing articles having shape memory, all changes in shape must be defined at the time that the shape memory is impressed. A subsequent alteration of the ultimate end use shape (the shape which the article assumes after heat activation) is therefor not possible. Further, it is difficult to accurately control the ultimate end use shape where the article is to assume a complicated shape.